The invention relates to a device for braking sample and defective sheets of a machine for processing flat or sheet-like printing materials, such as a printing machine, wherein a sheet is guided along a sheet-guiding part, and to a machine for processing flat or sheet-like printing materials, in particular, a printing machine, which is equipped with such a device.
Such machines, particularly printing machines, have pile or stacking stations wherein the sheets provided for further use, e.g., for further processing, are deposited. When such a machine is started up, whether for a new printing order or after an interruption in the printing operation, sheets are printed which do not yet have the desired quality and, in this respect, are defective and are referred to as defective sheets or rejects. These must not be deposited in the paper sheet pile or stack provided for further processing, but rather have to be ejected.
Furthermore, during operation of the machine, sample sheets have to be removed regularly, on the one hand, for keeping a running check on the quality of the printed image and, on the other hand, for documenting the quality of the printing within the framework of standards relating to the operating sequence, such as the standard ISO 9000.
For ejecting the sheets, for example, devices have become known heretofore which delay the release of the sheets, conveyed by a chain conveyor and retained on grippers, beyond a normal depositing position of the sheets in a pile or stack provided for further processing, i.e., the grippers open later than in the case of the formation of a sheet pile or stack for acceptable sheets.
After the sheets have been ejected, they have to be braked in order to permit them to be fed to a separate depositing location. Elastic stops which absorb the kinetic energy of the sheets have become known for this purpose. A disadvantage, on the one hand, is that, in the case of such heretofore known known devices, adaptation to different paper grades, such as paper grades of different thicknesses, or different sheet formats is only possible to a limited extent, if at all, and, on the other hand, is that there is a risk of damage to the sensitive sample sheets, in particular, when the kinetic energy of the sample sheet is absorbed exclusively by braking forces acting upon the leading edge of the sheet.
Furthermore known heretofore are brushes which brake the sheets by frictional forces between the bristles and sheets. A risk of the sheet becoming adversely affected exists here as well.
It is accordingly an object of the invention to provide a straightforward and cost-effective device for braking sample and defective sheets of a machine for processing flat or sheet-like printing materials which avoids the aforementioned disadvantages of the heretofore known devices of this general type.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a device for braking sample and defective sheets of a machine for processing sheet-like printing materials, comprising a sheet-guiding part for guiding a sheet therealong, a roller resting on the sheet-guiding part and being movable at least in a vertical direction, for braking a sheet guided between the sheet-guiding part and the roller.
In accordance with another feature of the invention, the roller is disposed upline of at least an approximately vertical stop for the sheet.
In accordance with a further feature of the invention, the roller is formed of soft elastic material.
In accordance with an added feature of the invention, the soft elastic material is rubber.
In accordance with an additional feature of the invention, the roller is preloaded elastically in the direction of the sheet-guiding part.
In accordance with yet another feature of the invention, the roller is equipped for being moved with a horizontal movement component and has an elastic preloading counter to a transporting direction of the sheet.
In accordance with yet a further feature of the invention, the braking device includes a spherically recessed element wherein the roller is mounted, the spherically recessed element, on a side thereof directed away from the roller, being formed with an inclined surface sloping upwardly relative to a transporting direction of the sheet, and being in supporting contact with a stationary guide part for displacement on the inclined surface, the spherically recessed element being preloaded elastically counter to the transporting direction of the sheet.
In accordance with yet an added feature of the invention, the braking device includes a structure for adjusting contact pressure of the roller on the sheet-guiding part.
In accordance with yet an additional feature of the invention, the structure for adjusting contact pressure of the roller on the sheet-guiding part is at least one vertically disposed adjusting screw which is in operational contact with the spherically recessed element via a helical spring.
In accordance with still another feature of the invention, the braking device includes structure for adjusting impact pressure of the roller against the inclined surface by at least one horizontally disposed adjusting screw which is in operational contact with the spherically recessed element via a helical spring.
In accordance with still a further feature of the invention, the adjusting screw is disposed in a threaded bore formed in the sheet-guiding part.
In accordance with still an added feature of the invention, the sheet-guiding part, with the spherically recessed element and the roller, is connected to a swivellable flap which is pivotable about a horizontal axis.
In accordance with still an additional feature of the invention, the adjusting screw for adjusting the contact pressure of the roller on the sheet-guiding part is disposed in a threaded bore formed in the swivellable flap.
In accordance with another aspect of the invention, there is provided a machine for processing sheet-like printing material, including a device for braking sample and defective sheets, comprising a sheet-guiding part for guiding a sheet therealong, a roller resting on the sheet-guiding part and being movable at least in a vertical direction, for braking a sheet guided between the sheet-guiding part and the roller.
In accordance with a concomitant feature of the invention, the machine is constructed as a printing machine. The objects of the invention are thus attained by a device of the general type mentioned in the introduction hereto which has a roller resting on the sheet-guiding part, being movable at least approximately in the vertical direction, and braking a sheet guided between the sheet-guiding part and the roller.
Due to the construction according to the invention of the device for braking sample and defective sheets, those sheets are deposited properly in a position which remains the same, and can easily be removed by hand as required without requiring an operator to be available at each ejection point. A sheet fed to the device according to the invention via the sheet-guiding part comes into contact with the vertically elastically mounted roller via the leading edge thereof, as a result of which the roller is raised, counter to the gravitational force acting upon it, by the thickness of the sheet and can be made to rotate. The sheet is braked slowly by friction between the sheet-guiding part and the roller, with the result that damage to the sheet is avoided.
A preferred embodiment provides that the roller be disposed upline of an at least approximately vertical stop for the sheet. In this case, a sheet guided between the sheet-guiding part and the roller is braked to the extent that damage thereto as it comes into contact with the following stop is reliably avoided. There is thus no need for any damping devices for the last-mentioned stop; however, such devices may be provided optionally. Once the sheet has sprung back from the stop, the roller is made to rotate again in the opposite direction of rotation, and the sheet is brought to a standstill between the sheet-guiding part and the roller. The kinetic energy of the sheet is thus absorbed over a comparatively long distance, and only low braking forces thus act upon the sheet, with the result that damage thereto is avoided.
The device is suitable for different paper grades of different thicknesses, particularly also for cardboards or pasteboards, because the position of the vertically elastically mounted roller is adapted to the thickness of a sheet guided between it and the sheet-guiding part, and the roller always butts against the sheet in order to absorb the kinetic energy thereof. The distance between the roller and the stop is in the order of magnitude of the gripper border of the sheet.
The roller is preferably formed of a soft elastic material, in particular rubber, which simultaneously provides a high coefficient of friction in order to absorb the kinetic energy of the sheet in an effective manner and to prevent the sheet from sliding along the roller without making the roller rotate.
While the roller can be raised solely counter to the weight thereof, a preferred embodiment provides that the roller be prestressed or preloaded elastically in the direction of the sheet-guiding part, in order to increase the braking forces acting upon the sheet and always to provide a desired contact pressure of the sheet in the direction of the sheet-guiding part.
It is further preferably provided that the roller also be able to be moved with a horizontal movement component and prestressed or preloaded elastically counter to the transporting direction of the sheet, with the result that damage to the leading edge of a sheet, in particular of a relatively thick sheet, e.g., a cardboard or pasteboard, as a result of the springing back of the roller as the sheet comes into contact with the roller is reliably avoided.
The roller is preferably mounted in a spherically recessed or indented element which, on a side thereof directed away from the roller, has an inclined surface sloping upwardly relative to the transporting direction of the sheet, and is in supporting contact with a stationary guiding part so that it is displaceable on the inclined surface, the spherically recessed element being prestressed or preloaded elastically counter to the transporting direction of the sheet. This forms, between the guide part and the spherically recessed element, a slide bearing which ensures longitudinal displaceability of the roller in order that, in particular, the leading edge of sheets of different thicknesses is not damaged and the sheets are simultaneously braked as they come into contact with the roller, in that the roller, which is prestressed elastically counter to the transporting direction of the sheet, is moved along the inclined surface in the direction of the sheet until the distance between the roller and the sheet-guiding part corresponds at least to the thickness of the sheet. When the sheet springs back from the stop, longitudinal displacement of the roller in the rearward direction beyond a point at which the distance between the roller and the sheet-guiding part corresponds to the thickness of the sheet is prevented by the slide bearing formed between the sheet-guiding part and the spherically recessed element, and the sheet is brought to a standstill by the roller.
In order to adapt the device according to the invention to different paper grades, and to adjust the desired removal position of each sheet brought to a standstill by the roller, it is preferably possible to adjust the contact pressure of the roller on the sheet-guiding part. It is possible to adjust the contact pressure of the roller, for example, by at least one vertically arranged adjusting screw, which is in supporting contact with the spherically recessed element via a helical spring and thus prestresses the roller with a variable force in the direction of the sheet-guiding part. It is also preferably possible to adjust the impact pressure of the roller against the slope by at least one horizontally arranged adjusting screw, which is in supporting contact with the spherically recessed element via a helical spring, and is disposed, for example, in a threaded bore formed in the sheet-guiding part.
One embodiment provides that the sheet guiding part, with the spherically recessed element and the roller, is connected to a swivellable flap which can be pivoted about a horizontal axis, in which case the device is in the operating position when the swivellable flap is closed, and the ejected sheet can be removed once the swivellable flap has been opened. In such a configuration, the adjusting screw, for adjusting the contact pressure of the roller on the sheet-guiding part, is preferably arranged in a threaded bore of the swivellable flap, in order to set the contact pressure of the roller on the sheet-guiding part in the operating position of the device according to the invention, with the swivellable flap closed.
The invention also relates to a machine which processes sheet-like printing materials and is equipped with a braking device of the aforementioned type.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for braking sample and defective sheets of a sheet-processing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: